Our current NPDES permit expired Sept. 30, 2011. NPDES permits are a 5 year term. Upon expiration, the old permit will be in effect until a new permit is issued. MPCA reviews current water quality standards and implements changes in permit limits at this time. Permit Terms
We were notified of our new proposed limits for our permit renewal in March of 2013. We have been working with our engineering consultant- Bolten & Menk and MPCA to address issues with the proposed limits and testing requirements.
Chloride limits will be the hardest issue to deal with. Currently the only technology for treatment is Reverse Osmosis systems to remove chloride. Very expensive capital equipment. Very expensive O&M. Still have a very concentrated waste stream to treat. Currently we discharge 700 ppm chloride to river. New limit is 261 ppm. Chlorides
Chloride comes from the regeneration of ion exchange water softeners ( home softeners salt). High levels in the river affect the biota. 3/4 of the chloride is coming from residential and commercial softeners.
Copper is in the wastewater through scaling of copper plumbing or some other sources of industrial discharges. We have no treatment capability to remove copper at the WWTF. We have seen effluent samples over the proposed monthly average limit and near the daily maximum limit. Copper
We have had a seasonal mass limit for phosphorus for some time. We treat with ferric chloride to reduce the effluent phosphorus with good success. New proposed limit would be a daily mass limit equal to 1 ppm on a daily average. Current seasonal limit = 8531 kg/yr.- $40,000/yr. Proposed daily limit= 4973 kg/yr.- $300,000/yr. Phosphorus
The additional treatment will also result in a large increase in biosolids production. This will increase our current solids handling and biosolids hauling requirements.
WET testing is a controlled test of the survival and reproduction of Fathead minnows and Ceria Daphnia Dubia in different concentrations of our effluent water to determine impact on the river. We are currently failing our WET testing. High chlorides are the likely source of impact. Whole Effluent Toxicity (WET)
Dissolved copper Dissolved mercury Chromium DEPH Nitrogen series Salty discharge series New Testing Parameters
We have submitted a compliance schedule to MPCA. Asking for extra time to do extensive testing to find sources, try source reduction to lower pollutants, look at available technologies and costs for treatment of the different pollutants. We are asking for 5 years to meet the new phosphorus limit so we can do a facility plan to identify all phosphorus sources and best treatment options including construction of new or expanded facilities. Options
We are asking for 10 years to meet the new copper limits. We need to do extensive testing to find sources and try reducing the pollutant at the source and do testing of the river to see if we are able to submit a site specific water quality standard for the Redwood River. If we cannot meet the limit we will be able to apply for a variance in 2023.
We are asking for 10 years to meet the new chloride limit. We need to look at further softening of the raw water at the MMU water treatment plant. This will reduce or eliminate the need for ion exchange water softeners- our largest source of chlorides. Potential ban on all ion exchange softeners. Hope for less restrictive water quality standards for chloride in the coming years.
There are many changes in our proposed permit with new and increased restrictions to discharge limits and they will be expensive to comply with. We have proposed what we feel is a process using best management practices until further testing and review is completed to be able to comply with the proposed MPCA limits. There is no fast or easy solution to know what we will need to do to meet the new limits. We will have to do a step by step approach to see how much source reduction we can achieve and what treatment options are most feasible. Conclusion